The world’s biggest offshore windfarm has officially opened in the Irish Sea, amid warnings that Brexit could increase costs for future projects.

Walney Extension, off the Cumbrian coast, spans an area the size of 20,000 football pitches and has a capacity of 659 megawatts, enough to power the equivalent of 590,000 homes.

The project is a sign of how dramatically wind technology has progressed in the past five years since the previous biggest, the London Array, was finished.

The new windfarm uses less than half the number of turbines but is more powerful.

Matthew Wright, the UK managing director of Danish energy firm Ørsted, the project’s developer, said: “It’s another benchmark in terms of the scale. This – bigger turbines, with fewer positions and a bit further out – is really the shape of projects going forward.”

The energy minister Claire Perry said the scheme would help the UK, the world’s number one in offshore wind installations, to consolidate its leadership and create thousands of high-quality jobs.

The supersizing of windfarms around the British coastline means Walney Extension will not hold its title for long.

ScottishPower’s East Anglia One will be bigger at 714MW when it opens in 2020. Ørsted itself has even larger schemes in the works, including Hornsea One and Two (1,200MW and 1,800MW, respectively) off the Yorkshire coast.